1. Field of the Invention
This invention relates to the field of semiconductor manufacturing and, more specifically, to an improved method and apparatus for a wafer carrier for chemical-mechanical planarization (CMP) usage.
2. Description of Related Art
Semiconductor devices are typically made up of several layers to improve density and reduce interconnection complexity. On each layer, devices such as Metal Oxide Semiconductor (MOS) transistors are formed on a silicon substrate. Metalized contacts and vias are formed by depositing metal materials such as aluminum at contact points. Layers stacked one upon another are interconnected through an elaborate interconnection scheme.
Semiconductor manufacturing processes typically consist of several steps. One of the most important step is the planarization of the layers of the interconnection structure. Nonplanar surfaces create poor optical resolution of subsequent photolithographic processing steps, which in turn, prohibits the printing of high density lines.
To ensure planar topography, various planarization techniques have been developed. One approach, known as chemical-mechanical planarization (CMP), employs polishing to remove excess materials formed on the surface of the semiconductor wafers. In a typical chemical-mechanical polishing method, as shown in FIG. 1a and FIG. 1b, a silicon substrate or wafer 100 is placed facing downward on an orbital motion table 110 covered with a flat polishing pad 120 which is coated with an active chemical mixtures commonly referred to as "slurry" 125. The wafer 100 is mounted upward to wafer pad 135 which is coupled to a backing plate 130. The backing plate 130 and the wafer 100 are held by a wafer carrier ring 140 to prevent them from slipping laterally. Wafer carrier ring 140 is annular and is usually made of polymer such as PBT or Delrin. A rubber bladder 150 holds wafer carrier ring 140 and stainless steel backing plate 130. Wafer carrier ring 140 is fastened to wafer carrier plate 260 by a set of screws 160.sub.I through 160.sub.P ("P" being a positive whole number). The rubber bladder 150 is sandwiched in between wafer carrier ring 140 and wafer carrier plate 260 providing the sealing. The downward force F acting upon the backing plate 130 and the rotational movement of the polishing pad 120 together with the slurry 125 facilitate the abrasive polishing and planar removal of the surface of the wafer 100.
One major problem with the conventional CMP technique is the presence of defects that impact die yield and product reliability. If, for example, the pressure needed to ensure a quality polish process is too high, the wafer carrier ring could undergo extensive bending. With the extensive bending, the potential for defect generation is exacerbated since the over-stressed portion of the wafer carrier ring will be out of plane with the wafer, affecting slurry flow and causing wafer CMP polish non-uniformity. Another problem associated with the conventional CMP technique is that the sealing of the rubber bladder may be adversely affected during operation, resulting in leakage. To check for leakage, regular preventive and maintenance (PM) checks are regularly performed. PM times reduce equipment availability.
Therefore, it is desirable to have an improvement on the chemical-mechanical polish head structure to reduce the bending and the leakage of the sealing.